Guile complains that the `define-checked` name is undefined when
running `make test_guile` using the Makefile defined in this
repository:

<https://git.sr.ht/~retropikzel/test-srfi-253/>

Something is wrong in the exporting of SRFI-253's names for Guile.

I don't know how to fix it.

Thank you,
Yuval Langer.